Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$44.51	13.602%	$50.5643	$50.56	$50.55	$50.60
Purchase #2	$131.72	9.680%	$144.4705	$144.47	$144.45	$144.50
Purchase #3	$99.96	12.656%	$112.6109	$112.61	$112.60	$112.60
Purchase #4	$125.30	13.538%	$142.2631	$142.26	$142.25	$142.30
Purchase #5	$150.94	4.153%	$157.2085	$157.21	$157.20	$157.20
Purchase #6	$38.50	3.568%	$39.8737	$39.87	$39.85	$39.90
Purchase #7	$56.30	11.325%	$62.676	$62.68	$62.70	$62.70
7 purchase totals =	$647.23		$709.6670	$709.66	$709.60	$709.80